Characteristics of the evolution of defect structure during phase transformations in the Pd-H system

The pattern of evolution of the defect structure in the Pd-H system during phase transformations is formulated on the basis of x-ray data. It is shown that once the random dislocations formed during phase transformations in the a phase reach their critical density, they assemble into dislocation walls. This process results in the formation of a cellular dislocation substructure in the α phase. After the formation of the cellular substructure in the α phase the random dislocations created during phase transformations climb into the hydride phase, thereby curtailing the evolution of defect structure in the α phase. The subsequent influx of dislocations into the β phase maintains continued evolution of the defect structure (from cellular to block dislocation substructure). Not until that time is it possible for the evolution of the defect structure in the α phase to terminate, culminating in the formation of a block substructure. The nature of the observed phenomenon is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1275–1281 (July 1997)     

Effects of high-j intruder states in the fine structure of superdeformed bands

All known cases of ΔI=4 bifurcation in superdeformed bands are analyzed on the basis of the theory proposed by the author in a previous paper [I. M. Pavlichenkov, Phys. Rev. C 55, 1275 (1997)]. It is shown that the high-j intruder single-particle states play a critical role in the phenomenon. The bands in which fine structure can be observed are predicted. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 759–764 (25 December 1997)     

Magnetization-odd nonreciprocal reflection of light from the magnetoelectric—ferromagnet LiFe5O8

Circular dichroism, which changes sign under magnetization reversal and exhibits a 120° periodicity, is observed in the reflection of light from the (111) plane of a noncentrosymmetric LiFe₅O₈ crystal in the transverse geometry k⊥M, where the linear Kerr effect is forbidden. It is shown that this phenomenon is due to the manifestation of optical magnetoelectric susceptibility and a Kerr effect of third order in the magnetization. The spectral dependences of the circular dichroism in the range 1.4–3.1 eV show that this phenomenon is of a resonance character. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 65–70 (10 January 1997)     

Cherenkov trapping of waves and discreteness of 6 π-kink motion in a long Josephson junction

The phenomenon of Cherenkov trapping of generalized Swihart waves by a moving vortex is established using an analytically solvable model. The quantization of the structure of the field of the trapped waves is manifested as quantization of the values of the velocity of the vortices. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 4, 318–322 (25 February 1999)     

Field-asymmetric transverse magnetoresistance in a nonmagnetic quantum-size structure

A new phenomenon is observed experimentally in a heavily doped asymmetric quantum-size structure in a magnetic field parallel to the quantum-well layers — a transverse magnetoresistance which is asymmetric in the field (there can even be a channge in sign) and is observed in the case that the structure has a built-in lateral electric field. A model of the effect is proposed. The observed asymmetry of the magnetoresistance is attributed to an additional current contribution that arises under nonequilibrium conditions and that is linear in the gradient of the electrochemical potential and proportional to the parameter characterizing the asymmetry of the spectrum with respect to the quasimomentum. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 380–385 (10 September 1998)     

Explosive luminescence of silver azide

Spectroscopic-kinetic investigations of the luminescence accompanying the explosive decomposition of silver azide are performed. A new phenomenon is observed: predetonation luminescence. A comparison of the predetonation luminescence spectrum with the band structure is in agreement with a model in which the exothermic reaction 2N ₃ ⁰ →N₆ provides the energy for the explosion. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 2, 101–103 (25 July 1997)     

Formation of amorphous carbon on melting of microcrystalline graphite by picosecond laser pulses

Observations of microcrystalline graphite subjected to picosecond laser pulses reveal the formation of a liquid phase with a subsequent transition to a uniform amorphous state of a surface layer upon solidification. This phenomenon is observed on a definite type of graphite and with the radiation incident on a plane parallel to the sixfold symmetry axis, and only for certain parameters of the laser pulse. A structural analysis of the amorphous phase is performed by electron microscopy and Raman scattering spectroscopy. A periodic structure with a period of the order of the wavelength of the heating pulse is formed in the heating region. The “rulings” of this periodic structure are oriented in the direction of polarization of the heating pulse. A study of the reflection kinetics of the probe laser pulse showed that the characteristic existence time of the liquid phase and of the solidification process is ∼10⁻¹⁰ s. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 10, 661–665 (25 November 1997)     

Influence of parity-forbiddenness in the onset of mixed valence state in Sm1−x GdxS

The electronic structure of Sm and Gd in Sm_1−x Gd_xS has been experimentally studied by the x-ray shift method. Besides the well known strong increase of Sm valence at x≈0.15 (associated with the electronic transition to the mixed valence state), a decrease of Sm valence for x⩾0.9 has been observed for the first time. This phenomenon is explained as due to the 4f-5d hybridization on neighboring Sm atoms involved in the onset of the mixed valence state, and is interpreted as a manifestation of parity violation forbiddenness. Fiz. Tverd. Tela (St. Petersburg) 39, 1017–1019 (June 1997)     

Ostwald step rule in films of metastable nanocrystalline alloys Fe-C prepared by pulsed plasma vaporization

Ferromagnetic nanocrystalline Fe(C) films were prepared by pulsed plasma vaporization. A comprehensive investigation of the structure and magnetic properties made it possible to identify the type of short-range order here and to establish the sequence of structural states occurring in these films in the process of thermal relaxation: fcc-Fe(C)→hcp-Fe(C)→bcc-Fe+C. On the basis of an analysis of the metastable phase diagrams using Ostwald’s rule, it is shown that the observed scenario of the structural transformations in these metastable nanocrystalline alloys Fe(C) is a natural phenomenon. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 727–732 (10 December 1999)     

Fermions at a half-quantum vortex

The spectrum of the fermion zero modes in the vicinity of a vortex with fractional winding number is discussed. This is inspired by the observation of the 1/2-vortex in high-temperature superconductors made by [J.R. Kirtley, C.C. Tsuei, M. Rupp et al., Phys. Rev. Lett. 76, 1336 (1996)]. The fractional value of the winding number leads to a frac-tional value of the invariant which describes the topology of the energy spectrum of fermions. This results in the phenomenon of the “half-crossing:” the spectrum approaches zero but does not cross it, being captured at the zero energy level. The similarity with the phenomenon of fermion condensation is discussed. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 729–734 (10 May 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Longitudinal critical current in a ferrite-type-II superconductor structure

The effect of the interaction of Abrikosov vortices with the magnetization on the longitudinal vortical instability in a layered ferromagnet-type-II superconductor structure is analyzed. It is shown that in the vicinity of the orientational phase transition in the magnet, where the transverse magnetic susceptibility is large, the magnitude of the longitudinal critical current in the structure can be almost 1.5 times smaller than in the isolated superconductor. The reason for this is compensation of stray field sources outside the superconductor by “magnetic charges” arising from a jump in the transverse magnetization on the surface of the magnet. A structure is considered in which the thickness of the superconductor significantly exceeds the London penetration depth of the magnetic field and the wavelength of the critical mode. For this reason (in light of the absence of high-quality bulk high-temperature superconductors), to experimentally study the described phenomenon it is necessary to use conventional low-temperature superconductors. Fiz. Tverd. Tela (St. Petersburg) 39, 231–235 (February 1997)     

Boltzmann spectral distribution or “infrared catastrophe” in the resonance radiation of a gas

The purely thermal infrared emission spectra of a resonance medium (sodium vapor) are investigated experimentally. It is shown that the emission intensity in the 2–3 μm range at temperatures of 600–1200 K is several orders of magnitude higher than the intensity obtained from the standard theory of resonance radiation transfer. This phenomenon can be conventionally termed an “infrared catastrophe.” The form of the recorded spectra and the absolute intensity of the emission in both the infrared and visible regions of the spectrum are in agreement with the theory developed by Yu. L. Zemtsov and A. M. Starostin, Zh. éksp. Teor. Fiz. 103, 345 (1993) [JETP 76, 186 (1993)], in which the Boltzmann spectral distribution of the population of the resonance level is proportional to exp(−ħω/T). Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 807–811 (10 June 1997)     

Critical experiments in the search for fermion condensation

The specific features of fermion condensation — a phase transition associated with the rearrangement of the one-particle degrees of freedom in strongly correlated Fermi systems — by which this phenomenon can be detected experimentally are discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 828–833 (10 June 1997)     

Nonlinear interaction of magnetoacoustic waves in yttrium orthoferrite

The phenomenon of energy transfer, both monotonic and oscillating, between the fundamental and higher harmonics of standing acoustic waves is observed during the laser generation of sound in YFeO₃ crystals. An analogous phenomenon for traveling light waves is well known in nonlinear optics. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 12, 789–792 (25 December 1999)     

Parametric interaction of volume magnetostatic waves in a ferrite film with spatiotemporal modulation of the magnetic field

Effects of the resonant Bragg scattering of magnetostatic backward volume waves on the periodic structure of a conductive meander pattern with an alternating current are analyzed theoretically and compared with experiment. It is shown that unlike a static grating, a dynamic grating causes a frequency shift of the scattered wave. It is proposed that this phenomenon be utilized for effective control of the intermodal conversion of magnetostatic waves. Zh. Tekh. Fiz. 68, 105–112 (May 1998)     

Noise-induced hypersensitivity to weak alternating signals

An example of the helpful role of noise in information transmission processes is the well-known phenomenon of stochastic resonance. This letter examines another such example — parametric-noise-induced giant amplification of ultraweak signals in a system with on-off intermittency. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 592–596 (25 April 1998)     

Nonequilibrium phase transition in quenched samples of Fe0.1TiTe2

The influence of the heat treatment of Fe_0.1TiTe₂ samples on the appearance of thermally induced “levitation” is investigated. It is postulated that this phenomenon is most probably caused by undamped fluctuations of the electric charge on the surface of particles of the material. Fiz. Tverd. Tela (St. Petersburg) 41, 680–683 (April 1999)     

High-pressure microwave discharge in an above-breakdown field. Streamer branching

A new effect — the splitting of the tips (branching) of a microwave streamer arising from a pre-existing dense plasma cloud in an above-threshold electric field — is obtained numerically on the basis of a planar two-dimensional model. The causes of this phenomenon and the factors suppressing it are found. An expression is obtained for the value of the cloud radius above which branching occurs. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 15–19 (10 January 1999)     

Localization and channeling of light in defect modes of two-dimensional photonic crystals

The spatial distribution of the electromagnetic field in a two-dimensional photonic crystal with a lattice defect is investigated. It is shown that in such a structure the field can be localized in a region smaller than one wavelength in size. The dependence of the spectrum of defect modes on the parameters of a two-dimensional photonic crystal is investigated. The light field at the exit of the photonic crystal possesses properties of a nonradiative mode, making it possible to achieve spatial resolution in the near-field much higher than the radiation wavelength. The possibilities of using this phenomenon in optical near-field microscopy to produce optical memory devices and to increase the efficiency of nonlinear optical interactions are discussed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 323–328 (10 September 1999)     

Effect of electron-electron interaction on thermoelectric power in impure metals

A new kinetic phenomenon related to the effect of electron-electron scattering on the thermoelectric coefficient η a conductor with a small electron mean free path l is considered. The effect is proportional to the electron-hole asymmetry factor (ε _Fτ)⁻¹ and the real part of the diffusion-enhanced Coulomb propagator with characteristic wave vectors of up to l ⁻¹. Unlike weak localization effects, in the two-dimensional case this effect results in a logarithmic temperature dependence of η and yields the major contribution to the differential thermoelectric power. Zh. éksp. Teor. Fiz. 111, 1738–1747 (May 1997)